A four-year-old boy with a genetic disorder has been killed by the flu and now his older brother is in the hospital with the same virus.

Jonah Rieben died on January 6 just hours after first showing symptoms, making him the first child to die from the flu in Ohio this season.

The boy who loved to play with his 16 adoptive siblings was born with Noonan syndrome, a genetic disorder that causes heart defects, developmental delays and short stature, and doctors are still investigating if his condition contributed to his death.

Now his parents who have spent years caring for children with rare, debilitating disorders are reeling as they fight such a common virus as the flu.

Jonah's older brother, who also suffers from a disorder, is in the hospital with a severe case of the flu that has been sweeping the US this season, killing at least 20 children and 85 adults.

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Jonah Rieben, four, became the first child to die from the flu in Ohio on January 6

His parents Valerie and Richard Rieben had less than a year with Jonah after adopting him from Bulgaria in February 2017

Jonah was the first of two children to die in Ohio from the flu. The second reported child death was of a one-year-old boy from Lucas County.

He died within hours of being brought to Dayton Children's Hospital after showing flu-like symptoms.

Jonah had spent less than a year with his new family after being born in Bulgaria and adopted by Valerie and Richard Rieben in February 2017.

He was the youngest of 17 children, 14 of who were adopted from Bulgaria, Ukraine and Uzbekistan and suffer from disorders.

The boy who loved music, car rides and chocolate smoothies was described in his obituary as 'the happiest when he was in the middle of the chaos and craziness of his large and loving family.'

Doctors are still investigating if Jonah's genetic disease contributed to his death.

He suffered from Noonan disorder, a genetic condition that causes heart defects and developmental delays.

A complete report by the medical examiner will take about six months to determine the exact cause of his death.

Typically someone would show signs of the flu before it gets to the point of death, leading experts to believe that Jonah's condition could have made an impact.

His father Richard said: 'You know, you belong to the "special needs parents" group. You belong to the "big family" group. The group I didn't think I was ready to join was the group that has lost a young child.'

Jonah was the youngest of 17 children (pictured together at Christmas 2017), 14 of whom were adopted and have medical conditions

He showed flu-like symptoms just hours before being rushed to Dayton Children's Hospital where he died. He had a genetic disorder that is thought to have contributed to his death

Jonah's death comes as this season's massive flu outbreak is devastating the US.

This season the flu has killed at least 20 children and more than 85 adults in the US, according to the CDC.

The rate of hospitalizations almost doubled in a week, leaving hospitals overcrowded, understaffed and turning some patients away.

Experts warn that infants and elderly people are the most vulnerable. The flu is now widespread in more than 46 states as the outbreak reaches his peak, making it one of the worse flu seasons in years.

It is especially dangerous because while most people suffering from the flu experience fever, chills, muscle aches, cough, congestion, runny nose, headaches and fatigue, not all those infected show symptoms.